U.S. patent number 7,512,348 [Application Number 11/313,800] was granted by the patent office on 2009-03-31 for image forming apparatus with a toner replenishment feature.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Yusuke Ishida, Kazushige Nishiyama, Hideaki Suzuki.
United States Patent |
7,512,348 |
Suzuki , et al. |
March 31, 2009 |
Image forming apparatus with a toner replenishment feature
Abstract
An image forming apparatus includes: a developing unit for
developing a latent image on an image bearing member by using a
developer containing toner and a carrier; and a detecting unit for
detecting a density of a detection reference toner image, wherein
detection results obtained by the detecting unit are employed to
control a toner replenishment operation for the developing unit,
and wherein, when the detection results obtained by the detecting
unit is equal to or smaller than a predetermined value, a residual
toner amount determination mode is performed. The residual toner
amount determination mode includes: a toner replenishment step of
performing an operation for replenishing toner; a detecting step of
performing the detecting unit to detect the density of the
detection reference toner image; and a comparison step of comparing
a first detection result obtained at the detection step with a
second detection result obtained by the detecting unit before said
toner replenishment step is performed the first time, and for which
respective performance of the steps is enabled while an image
forming operation is halted, and wherein, based on the results
obtained at said comparison step, whether the residual toner amount
determination mode should be continued is determined.
Inventors: |
Suzuki; Hideaki (Ibaraki,
JP), Ishida; Yusuke (Ibaraki, JP),
Nishiyama; Kazushige (Chiba, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
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Family
ID: |
34315698 |
Appl.
No.: |
11/313,800 |
Filed: |
December 22, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060159474 A1 |
Jul 20, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10935086 |
Sep 8, 2004 |
7010237 |
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Foreign Application Priority Data
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Sep 22, 2003 [JP] |
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2003-330054 |
Sep 22, 2003 [JP] |
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2003-330057 |
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Current U.S.
Class: |
399/27 |
Current CPC
Class: |
G03G
15/0822 (20130101); G03G 15/553 (20130101); G03G
15/556 (20130101); G03G 2215/00037 (20130101); G03G
2215/0177 (20130101); G03G 2215/0609 (20130101) |
Current International
Class: |
G03G
15/08 (20060101) |
Field of
Search: |
;399/27,49 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1218205 |
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Jun 1999 |
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CN |
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1253480 |
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Oct 2002 |
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EP |
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62-299876 |
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Dec 1987 |
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JP |
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4-066986 |
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Mar 1992 |
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JP |
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5-66669 |
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Mar 1993 |
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JP |
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8-202091 |
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Aug 1996 |
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JP |
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9-80893 |
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Mar 1997 |
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JP |
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2001-194840 |
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Jul 2001 |
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JP |
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Other References
Computer Translation of cited document JP05-066669a. cited by
examiner .
Japanese Notification of Reason for Refusal dated Nov. 4, 2008 in
Japanese Application No. 2003-330057, and an English-language
translation thereof. cited by other.
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Primary Examiner: Grainger; Quana M
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a divisional of application Ser. No.
10/935,086, filed Sep. 8, 2004 now U.S. Pat. No. 7,010,237.
Claims
What is claimed is:
1. An image forming apparatus comprising: a developing device for
developing an electrostatic image on an image bearing member using
a developer containing a toner and a carrier; a detection device
for detecting a density of a detection toner image; and a
controller for controlling a toner replenishment operation to said
developing device on the basis of a result detected by said
detection device, wherein, when a result detected by said detection
device becomes equal to or smaller than a predetermined value, said
controller performs a residual toner amount detection mode while
interrupting an imaging forming operation, wherein, in the residual
toner amount detection mode, there are performed: a first step of
performing the toner replenishment operation; and a second step of,
after said first step, forming a toner patch by said developing
device, and detecting said toner patch by said detection device;
wherein said controller performs said residual toner amount
detection mode again if the result detected by said detection
device in said second step is equal to or smaller than the
predetermined value, and terminates said residual toner amount
detection mode if the result detected by said detection device in
said second step is larger than the predetermined value, and
wherein, when the residual toner amount detection mode is performed
a plurality of times, said controller performs a replenishment
control in such a manner that a period of time for the toner
replenishment operation during an early phase mode of the plurality
of residual toner amount detection modes is longer than a period of
time for the toner replenishment operation during a late phase
mode, of the plurality of residual toner amount detection modes,
after the early phase mode.
2. An image forming apparatus according to claim 1, wherein said
controller notifies an absence of toner, if the result detected by
said detection device in said second step is equal to or smaller
than the reference value after said residual toner amount detection
mode is repeated a predetermined number of times.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus, such
as a copier or a laser beam printer, that employs an electrostatic
recording system or an electrophotographic system.
2. Related Background Art
A two-component developing method that uses, as a developer, a
mixture of a non-magnetic toner and a magnetic carrier has been
widely employed for conventional electrophotographic image forming
apparatuses, especially image forming apparatuses for performing
chromatic color image forming. Compared with other currently
proposed developing methods, the two-component developing method is
superior in the stability of image quality and the durability of
the apparatus. However, since as image forming is performed only
toner is consumed, the supply of an appropriate toner must be
replenished, as needed, and the toner density (the ratio of the
weight of toner to the total weight of a developer) must be
adjusted within an appropriate range. For the stabilization of
image quality, it is extremely important that the toner density be
adjusted within an appropriate range, and to achieve that
objective, various methods have been proposed and put to practical
use.
For example, a photodetecting method, an inductance detecting
method, a patch detecting method, and a video counting method have
been proposed and practically employed.
Above all, the patch detecting method is a method whereby the
density of a reference toner image (hereinafter referred to as a
patch image) formed on a photosensitive member is read using a
light source, provided opposite the surface of the toner image, and
a sensor, for receiving light reflected by the surface; and
whereby, to adjust toner density, toner is replenished based on a
value output by the sensor. Therefore, since a sensor need not be
provided for each developing device, and since a cost savings can
thus be realized, the patch detecting method has been widely
employed.
When an image forming apparatus is employed for an extended period
of time, toner supplied from a toner storage unit is consumed, so
that the amount of toner remaining must constantly be monitored,
and a user must be requested to replenish the supply as necessary.
Conventionally, residual toner amount detecting means of a
piezoelectric type, an antenna type and a photodetecting type have
been proposed and have been employed. Another method is a toner
presence/absence detecting method using the patch detecting method.
When, for example, the detection output for the density of a patch
image is equal to or smaller than a predetermined value, or when
the value of a patch image density obtained after a forced toner
replenishment operation has been performed is less than a
predetermined value, it is determined that there is an absence of
toner (for example, Japanese Patent Application Laid-Open No.
H5-66669). And since only one sensor is required, both for
detecting the presence/absence of toner and for controlling toner
density, a special sensor for monitoring the toner supply is not
required, making this is a very superior, cost efficient
method.
However, using this method, a determination is made merely as to
whether a value detected for patch image density is greater or
smaller than a predetermined value, and it is difficult to
ascertain whether toner has actually been exhausted or whether a
factor other than toner density is responsible for a reduction in
the patch image density. To resolve this problem, instead of the
above method that employs, during normal operation, a value
detected and output for the patch image density, a method that
determines whether a detected output, obtained following the
performance of a forced toner replenishment operation, exceeds a
predetermined value can be employed to determine the
presence/absence of toner. With this method, so long as there is
toner remaining in the toner storage unit, the density of a patch
image is absolutely increased following the forced replenishment of
toner. Therefore, regardless of the state of the developer, whether
toner is present or absent can correctly be ascertained.
However, when a fixed value is employed as a threshold value for
determining the presence/absence of toner, the following problem
has arisen: Whereas for a patch detecting operation performed
during a normal toner replenishment process a reference signal
value is corrected in accordance with the conditions encountered
during that specific situation, when a fixed threshold value is
used during an operation performed to detect the presence/absence
of toner, a patch image density signal fluctuates, depending on the
current situation, and the difference between the threshold and the
detected value may be too large, or too small, so that the
presence/absence of toner cannot correctly be determined.
Furthermore, when the environment of the image forming apparatus is
changed, the .gamma. characteristics of a developer also fluctuate,
and relative to the toner density the sensitivity of the patch
image density signal is also changed. Further, since the .gamma.
characteristics of the developer also change in accordance with the
accumulative use period for the developer, accordingly, the
sensitivity of the patch image density signal relative to the toner
density is changed. As is described above, when relative to the
toner density the sensitivity of the patch image density signal is
changed, the amount of change in the patch image density signal
varies relative to the same change in the toner density. In this
case also, when the threshold value is fixed, the presence/absence
of toner cannot be correctly detected.
SUMMARY OF THE INVENTION
It is, therefore, one objective of the present invention to provide
an image forming apparatus that more correctly and reliably
determines, by the detection of a detecting reference toner image,
the presence/absence of the toner remaining in developing
means.
To achieve this objective, a preferred image forming apparatus
comprises:
developing means for developing a latent image on an image bearing
member by using a developer containing toner and a carrier;
detecting means for detecting a density of a detection reference
toner image; and
control means for control a toner replenishment operation for said
developing means, based on detection results obtained by the
detecting means to,
wherein, when the detection results obtained by the detecting means
is equal to or smaller than a predetermined value, the control
means performs a residual toner amount determination mode, that
includes
a toner replenishment step of performing an operation for
replenishing toner,
a detecting step of performing the detecting means to detect the
density of the detection reference toner image, and
a comparison step of comparing a first detection result obtained at
the detection step with a second detection result obtained by the
detecting means before the toner replenishment step is performed
the first time, and for which repetitive performance of the steps
is enabled while an image forming operation is halted, and
wherein, based on the results obtained at the comparison step, the
control means determines whether the residual toner amount
determination mode should be continued.
Another preferred image forming apparatus comprises:
developing means for developing a latent image on an image bearing
member by using a developer containing toner and a carrier;
detecting means for detecting a density of a detection reference
toner image; and
control means for controlling a toner replenishment operation for
the developing means, based on detection results obtained by the
detecting means,
wherein, when the detection results obtained by the detecting means
is equal to or smaller than a predetermined value, the control
means performs a residual toner amount determination mode, that
includes
a toner replenishment step of performing a toner replenishment
operation,
a detection step of performing the detecting means to detect the
density of the detection reference toner image, and
a comparison step of comparing the results obtained at the
detection step with a reference value, and for which repetitive
performance of the steps is enabled while an image forming
operation is halted,
wherein, based on results obtained at the comparison step, the
control means determines whether the residual toner amount
determination mode should be continued, and
wherein the control means reduces an amount of toner to be
replenished, so that the amount of toner to be replenished at the
second and following times in the residual toner amount
determination mode is smaller than the amount of toner to be
replenished at the first time in the residual toner amount
determination mode.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram for explaining an image forming apparatus
according the first to fourth embodiments of the present
invention;
FIG. 2 is a diagram for explaining a developing device according to
the first to fourth embodiments of the present invention;
FIG. 3 is a flowchart for explaining a toner replenishment
operation according to the first to fourth embodiments of the
present invention;
FIG. 4 is a flowchart for explaining a toner presence/absence
detection mode according to the first to fourth embodiments of the
present invention;
FIG. 5 is a diagram for explaining a relationship between a fixed
value Vtrgt and a signal value Vsig;
FIG. 6 is a graph for explaining a relationship between a variable
value Vtrgt and a signal value Vsig;
FIG. 7 is a graph for explaining a relationship between an absolute
moisture amount and the toner density sensitivity of a
developer;
FIG. 8 is a graph showing a relationship between the number of
passage sheets accumulated, which is consonant with a cumulative
period for the use of a developer, and toner density
sensitivity;
FIG. 9 is a specific, vertical cross-sectional view of the
schematic configuration of an image forming apparatus according to
a fifth embodiment of the present invention;
FIG. 10 is a specific, vertical cross-sectional view of the
structure of the layers on a photosensitive drum;
FIG. 11 is a vertical cross-sectional view of the structure of a
developing device;
FIG. 12 is a diagram for explaining unit block replenishment
according to the fifth embodiment;
FIG. 13 is a flowchart for explaining a toner presence/absence
detection operation using a video counting method according to the
fifth embodiment;
FIG. 14 is a flowchart for the toner replenishment processing that
employs a video counting method and a patch detection method
according to the fifth embodiment;
FIG. 15 is a flowchart showing a toner presence/absence detection
operation according to the fifth embodiment;
FIG. 16 is a flowchart for explaining a residual toner amount
detection sequence according to the fifth embodiment;
FIG. 17 is a flowchart for explaining a residual toner amount
detection sequence according to a sixth embodiment of the present
invention; and
FIG. 18 is a flowchart for explaining a toner presence/absence
detection mode according to the second embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will now be
described while referring to the accompanying drawings.
First Embodiment
First, an image forming apparatus according to a first embodiment
of the present invention will be described. As is shown in FIG. 1,
the image forming apparatus of this embodiment is a rotating
development system. A rotary member 18 includes a black developing
device 1K, a yellow developing device 1Y, a magenta developing
device 1M and a cyan developing device 1C, and is rotatable by a
motor (not shown). To form a black toner image on a photosensitive
drum 28, the black developing device 1K performs developing at a
development position facing the photosensitive drum 28. Similarly,
to form a yellow toner image, the rotary member 18 is rotated
90.degree. and the yellow developing device 1Y is moved to the
development position. The same process is performed to form magenta
and cyan toner images.
The entire operation of the image forming apparatus in a full color
image forming mode will now be explained. It should be noted that
the developing device 1 is a general term for the black developing
device 1K, the yellow developing device 1Y, the magenta developing
device 1M and the cyan developing device 1C. In FIG. 1, an exposing
device 22, such as a laser, exposes the surface of the
photosensitive drum 28, which is electrified by a primary charging
device 21, and forms a latent image on the photosensitive drum 28.
The developing device 1 holding a predetermined toner develops the
latent image on the photosensitive drum 28 and forms a toner image.
The toner image is transferred to an intermediate transferring
member 24 by the primary transferring bias of a primary
transferring and charging device 23a. For the formation of a full
color image, first, a black toner image is formed by the black
developing device 1K and temporarily transferred to the
intermediate transferring member 24. Then, the rotary member 18 is
rotated 90.degree. to move the yellow developing device 1Y to the
development position, and a yellow toner image is formed on the
photosensitive drum 28. The yellow toner image is then transferred
to the black toner image on the intermediate transferring member
24, superimposing these images. This process is thereafter
performed for the magenta developing device 1M and the cyan
developing device 1C, and a predetermined full color image is
formed on the intermediate transferring member 24. Thereafter, by
employing the second transferring bias of a secondary transferring
and charging device 23b, the full color image that is obtained is
transferred from the intermediate transferring member 24 to a
recording sheet 27 conveyed by a transfer sheet conveying belt 25.
Subsequently, the image bearing sheet 27 is separated from the
transfer sheet conveying belt 25 and is pressurized/heated by a
fixing device 26 to obtain a permanent image. Following the
completion of the primary image transfer, any toner remaining on
the photosensitive drum 28 is removed by a first cleaner 29a, and
following the completion of the secondary image transfer, any toner
remaining on the intermediate transferring member 24 is removed by
a second cleaner 29b. The image forming apparatus is thus prepared
for the next image forming operation.
A detailed description of the structure of the developing device 1
will now be given while referring to FIG. 2.
The developing device 1 holds a two-component developer formed of
non-magnetic toner and magnetic carriers, and the initial density
of the developer (the ratio of the weight of toner to the total
weight of the developer) is adjusted to 7%. This value should be
appropriately adjusted in accordance with the charge amount of
toner, the size of carrier particles and the configuration of the
image forming apparatus, and need not always be 7%.
The developing, open area of the developing device 1 faces the
photosensitive drum 28, and in the open area, a rotatable
developing sleeve 3 is arranged and is partially exposed. The
developing sleeve 3 is formed of a non-magnetic material, and
encloses a fixed magnet 4 used as magnetic field generation means.
During the development operation, the developing sleeve 3 is
rotated in a direction indicated by an arrow in FIG. 1, holds as
layers the two-component developer stored in a developing container
2, and carries and supplies the developer to the development area
facing the photosensitive drum 28. As a result, an electrostatic
latent image is developed on the photosensitive drum 28. And after
the electrostatic latent image has been developed, the developer is
conveyed, as the developing sleeve 3 is rotated, and is collected
in the developing container 2, for which a first agitation screw 2a
(nearer the developing sleeve 3) and a second agitation screw 2b
(farther from the developing sleeve 3) are provided. Within the
developing container 2, the developer is stirred circularly by the
first agitation screw 2a and the second agitation screw 2b and is
mixed with toner supplied from a toner cartridge 5, which functions
as a toner storage unit. Since all the toner cartridges 5, for
black, yellow, magenta and cyan, are substantially cylindrical,
they can easily be attached to or detached from the rotary member
18 and the developing devices 1.
Toner retained in the toner cartridge 5 is carried through a
release port 6 to a toner supply unit 9, provided for the
developing container 2, and the supply of toner to the developing
container 2 is accomplished by the rotation of a toner supply
member, a toner supply screw 8. The amount of toner supplied to the
developing container 2 is substantially determined in accordance
with the length of time the toner supply screw 8 is rotated, which
is controlled by a toner supply control means 50 that will now
specifically be described.
Since with each repetition of the image forming operation, toner in
the developing container 2 is consumed and its density In the
developer is reduced, the supply of toner must be replenished, as
needed, to maintain a density that falls within a predetermined
range. According to the present invention, a reference toner image
is formed on the photosensitive drum 28, and a density signal, for
the reference toner image, is prepared from results obtained by a
density detection sensor and is compared with a previously stored
initial reference signal, and based on the comparison results, the
period the toner supply unit 9 is driven is controlled by the toner
supply control means 50.
When the patch detection process is performed, an electrostatic
latent image having a predesignated size is formed, as the
reference toner image, on the photosensitive drum 28, and is
developed by applying a predetermined development contrast voltage.
Then, a density signal Vsig for the obtained reference toner image
is prepared using the results obtained by an optical sensor 90
positioned facing the photosensitive drum 90, and its value is
compared with the value of an initial reference signal Vref,
previously recorded in memory. If Vsig-Vref<0, it is determined
that the density of the patch image is low, i.e., the developer
density is low, and based on the difference between Vref and Vsig,
the amount of toner required for replenishment and the rotation
period for the toner supply screw 9 are determined. On the other
hand, when Vsig-Vref.gtoreq.0, it is determined that the density of
the patch image is high, i.e., the developer density is high, and
the halted state of the toner supply screw 9 is maintained.
In this embodiment, the density signal is detected for the
reference toner image on the photosensitive drum 28. However, the
reference toner image formed on the photosensitive drum 28 may be
transferred to the intermediate transferring member 24, and the
density signal for the transferred image may be detected by an
optical sensor located near the intermediate transferring member
24.
A toner presence/absence detection process for this embodiment will
now be described. In this embodiment, a sensor for detecting the
presence/absence of toner is not provided for the toner cartridges
5 or the toner supply units 9, and a sensor used for patch
detection is also for employed to detect the presence/absence of
toner. With this arrangement, the costs required to provide the
toner presence/absence detection sensors can be eliminated.
The value of density signal Vsig, which is detected in the patch
detection mode during normal operation, is compared with a lower
limit value Vlimit (Vsig>Vlimit), which is predesignated for the
density signal, to determine whether the value of density signal
Vsig is less than the lower limit value Vlimit. When the value of
density signal Vsig exceeds the lower limit value Vlimit, it is
assumed that sufficient toner remains in the toner cartridge 5, and
difference Vsig-Vref is calculated to determine the rotation period
for the toner supply screw 9.
When the value of density signal Vsig is equal to or smaller than
the lower limit value Vlimit, it is assumed that the amount of
toner remaining in the toner cartridge 5 has been reduced. However,
since the patch density may vary in accordance with a factor other
than toner density, such as a triboelectricity fluctuation or a
photosensitive drum 28 potential change, the danger exists that the
presence/absence of toner will be determined based only on the
toner density detected during a normal patch operation.
Therefore, in this embodiment, when it is determined, by the patch
detection process performed during normal operation, that the value
of patch density signal Vsig is equal to or smaller than the lower
limit value Vlimit, the normal image forming operation is
temporarily halted, and is shifted to a special mode (a toner
presence/absence detection mode) for determining the
presence/absence of toner. In the toner presence/absence detection
mode, the presence/absence of toner in the toner cartridge 5 is
ascertained. This processing will be explained while referring to
FIG. 3.
The toner presence/absence detection mode will now be specifically
described while referring to FIG. 4.
When the toner presence/absence detection mode is entered, first, a
patch density signal Vlast, which is obtained during normal
operation immediately before the toner presence/absence detection
mode is entered, is read from a nonvolatile memory (not shown), and
as is represented by the following expression (1), a threshold
value Vtrgt, which is greater, by a predetermined amount, than
signal value Vlast, is obtained in order to determine whether toner
is present or absent. In expression (1), the threshold value Vtrgt
is represented at a level obtained by performing a ten bit
conversion of the drive voltage, 3.3 V, for a sensor.
Vtrgt=Vlast+34 (1)
The developing device 1 for determining the presence or absence of
toner is shifted to the development position, and the toner supply
screw 9 is rotated for three seconds to forcibly replenish toner.
At the same time, a patch image is formed on the photosensitive
drum 28, and the density signal Vsig is detected by the optical
sensor. When Vsig.gtoreq.Vtrgt, it is determined that toner is
present in the toner cartridge 5, and thereafter, the toner
presence/absence detection mode is terminated and the processing is
returned to normal. When Vsig<Vtrgt, the toner supply screw 9 is
again rotated for four seconds to replenish toner, and at the same
time a patch image is formed to detect the density signal. This
operation is repeated until Vsig.gtoreq.Vtrgt is established. When
Vsig<Vtrgt is unchanged, even though this operation is repeated
twelve times, it is determined that no toner is present in the
toner cartridge 5, and a message, such as "no toner", is displayed
In the operating section of the main body of the image forming
apparatus.
A detailed explanation will now be given for one reason that the
threshold value Vtrgt, used to determine the presence/absence of
toner, is determined based on the patch density signal Vlast that
is obtained during normal operation immediately before the toner
presence/absence detection mode is entered.
For the image forming apparatus In this embodiment, which controls
the amount of toner replenished based on the value detected for the
patch density signal, the amount of toner replenished is controlled
by detecting the density of a patch image that is formed at the
development step or at the development step and the transferring
step. Therefore, the density of toner in the developing device may
vary greatly due to a change in the characteristics of the
developer. For example, since the patch image density is reduced as
the charge amount of developer is increased, the amount of toner
replenished is increased, even though the actual toner density is
not low, so that in the developing device, the density of the toner
would be increased excessively. As means for resolving this
problem, a sensor, such as an optical sensor or an inductance
detection sensor, for directly detecting the density of toner in
the developing device is provided for the main body of the image
forming apparatus. This sensor is employed as a limiter for the
toner density, and when the toner density exceeds an appropriate
range, a reference signal Vref for patch detection is corrected.
Then, after the reference signal Vref for patch detection is
corrected, the value of patch density signal Vsig approaches the
reference value Vref and the two converge, as is shown in FIG. 5,
and an excessive increase in the toner density is suppressed.
However, if the threshold value Vtrgt, used for detection of the
presence or absence of toner, is still maintained as fixed when the
reference Vref for patch detection is corrected, a difference
between the value of signal Vsig and the threshold value Vtrgt
varies between when the reference signal Vref is corrected and when
it is not corrected, and the presence/absence of toner may not be
detected correctly. According to the example In FIG. 5, when the
reference signal Vref is corrected, the difference between its
value and the threshold value Vtrgt is increased, and
Vsig.gtoreq.Vtrgt is not obtained through the performance, a
predetermined twelve times, of the forced toner replenishment
operation in the toner presence/absence detection mode. As a
result, though toner is present in the developing device, it may
erroneously be determined that toner is absent.
To avoid this erroneous determination, the patch density signal
Vlast, which is obtained, during the normal image forming
operation, immediately before the toner presence/absence detection
mode is entered, need only be employed as a reference value, a
value greater, by a predetermined amount, the value of density
signal Vlast prepared as the threshold value Vtrgt and used for the
detection of the presence/absence of toner. As a result, as is
shown in FIG. 6, an appropriate difference between Vsig and Vtrgt
is maintained, and the presence/absence of toner can be determined,
regardless of whether the reference signal Vref is corrected. In
this case, the value of signal Vsig that is used for the
determination "Vsig.gtoreq.Vlimit?" in the flowchart in FIG. 3 may
be employed as the patch density signal that is obtained, during
the normal image forming operation, immediately before the toner
presence/absence detection mode is entered.
In this embodiment, a coefficient used for calculation of the
threshold value Vtrgt is designated as is represented in expression
(1), and the forced toner replenishment time, in the toner
presence/absence detection mode, and the number of replenishment
repetitions are designated as described above. However, these
numerical values are optimally set, depending on the configuration
of the image forming apparatus and the developer that is to be
employed.
As is described above, since the processing performed, as in this
embodiment, by the image forming apparatus that employs the patch
detection method to determine the presence/absence of toner in the
toner storage unit, even when the reference signal for patch
detection is corrected, the presence/absence of toner can be
correctly detected. As a result, an image forming apparatus can be
provided that will perform reliably for an extended use period of
time.
Second Embodiment
The feature of a second embodiment is that a threshold value, for a
patch image density signal for determining the presence/absence of
toner, can be obtained based on a density signal for a first patch
image that is formed in a toner presence/absence detection
mode.
When the message "no toner" is displayed, a toner cartridge is
exchanged for a new one, and the toner presence/absence detection
mode is again started to cancel the no toner message. However,
during this process, if the developer is left as it is for a long
time following the display of the no toner message and before the
toner presence/absence detection mode is restarted, the
triboelectricity in the developer fluctuates, and the density of
the first patch image formed in the toner presence/absence
detection mode will be changed greatly, when compared with the
density of a patch image formed during normal operation immediately
before the toner presence/absence detection mode is entered.
Therefore, when, as in the first embodiment, the threshold value is
determined based on the patch image density signal obtained during
normal operation immediately before the toner presence/absence
detection mode is entered, the presence or absence of toner may not
be detected correctly.
Therefore, in the second embodiment, as is shown in FIG. 18, when
the operating mode is shifted to the toner presence/absence
detection mode, the patch density is again detected before the
first toner replenishment operation is performed, and the detected
value is employed as a patch density signal Vlast. Through this
processing, the state immediately before the toner replenishment
operation is performed can be accurately identified, and the
presence or absence of toner can be detected more correctly,
regardless of how long the developer is left as it is.
Third Embodiment
The feature of a third embodiment is that an environment detection
sensor (temperature/humidity detection means 70) is provided to
detect the temperature and humidity in the main body of the image
forming apparatus, and that a threshold value used in a toner
presence/absence detection mode is determined based on the absolute
amount of moisture indicated by the detection results.
When an environment is changed and the absolute amount of moisture
in the air is altered, the .gamma. characteristics of a developer
are changed. Accordingly, relative to the toner density, the degree
of change in the patch density signal, i.e., the toner density
sensitivity, fluctuates. Generally, the .gamma. characteristics
tend to become more outstanding as the absolute amount of moisture
rises, and as is shown in FIG. 7, the toner density sensitivity
tends to increase.
Thus, when in the toner presence/absence detection mode a
predetermined amount of toner is furnished to replenish the
developing device 5 supply, the degree to which the patch density
signal is changed varies, depending on the environment wherein the
image forming apparatus is installed. For example, since toner
density sensitivity is reduced in low humidity, when in such
environment the toner supply is replenished by a predetermined
amount, the degree of change In the patch density signal is
reduced, compared with an environment wherein the humidity is high.
Therefore, when a fixed threshold value is employed to determine
the presence/absence of toner, more toner will be required to
exceed the threshold value than when the toner supply is
replenished in a high humidity environment. Therefore, an erroneous
toner presence/absence determination will be made, and an excessive
increase in the toner density will occur.
To resolve this problem, in this embodiment, the threshold value
used in the toner presence/absence detection mode is appropriately
adjusted in accordance with the toner density sensitivity, which
fluctuates in consonance with the absolute amount of moisture
detected. A specific control method will now be described.
In the third embodiment, as in the first embodiment, a threshold
value Vtrgt is determined based on a patch image density signal
Vlast obtained, during normal operation, immediately before the
toner presence/absence detection mode is entered. An expression for
determining the threshold value Vtrgt is defined as follows.
Vtrgt=Vlast+A (2)
The coefficient "A" In expression (2) is a variable, and an
appropriate value is selected in accordance with the absolute
amount of moisture. The relationship between the absolute amount of
moisture and the coefficient A is shown in Table 1.
TABLE-US-00001 TABLE 1 Absolute amount of moisture Coefficient A 0
g or greater, and smaller than 3.1 g 26 3.1 g or greater, and
smaller than 5.8 g 30 5.8 g or greater, and smaller than 10.1 g 34
10.1 g or greater, and smaller than 15.9 g 38 15.9 g or greater
42
When the threshold value Vtrgt is determined by using expression
(2), in a low humidity environment, the presence/absence of toner
can be determined in accordance with a smaller change in a patch
density signal. Therefore, the presence/absence of toner can be
correctly detected in consonance with the toner density sensitivity
of the developer. The same thing can be applied for a high humidity
environment.
It should be noted that the coefficient A is not limited to the
values shown in Table 1, and an optimal value can be designated,
depending on the configuration of the image forming apparatus and
the developer that is to be employed.
As is described above, since the threshold value used in the toner
presence/absence detection mode is appropriately selected in
accordance with the toner density sensitivity of the developer,
which varies in consonance with the absolute amount of moisture,
the detection of the presence/absence of toner can be correctly and
stably performed, without being affected by the environment wherein
the image forming apparatus is installed.
Fourth Embodiment
The feature of a fourth embodiment is that measuring means, for
measuring a time period for using the two-component developer
retained in a developing storage unit, and a nonvolatile memory,
used to store a cumulative value for the use period, are provided
for the image forming apparatus, and that a threshold value, used
in a toner presence/absence detection mode, is determined based on
a cumulative period (obtained by developer use history detection
means 60), for the use of the developer, that is stored in
memory.
Since as the cumulative period for the use of a developer is
increased, deterioration of the developer occurs and the .gamma.
characteristics of the developer are altered, accordingly, the
amount of change in a patch density signal is relative to the toner
density, i.e., the toner density sensitivity is altered. Generally,
as the use period time is increased, the .gamma. characteristics
tend to become outstanding, and as is shown In FIG. 8, the toner
density sensitivity tends to be increased.
Then, when in the toner presence/absence detection mode a
predetermined amount of toner is used to replenish the developing
device 1, changes in the patch density signal will differ,
depending on how long the developer has been used. For example, for
a developer that has been used for an extended period and has
suffered considerable, cumulative deterioration, the toner density
sensitivity is high, and when to replenish the toner a
predetermined amount is added, the degree of change in the patch
density signal will be greater than in the initial state of the
developer. In this case, when a fixed threshold value is maintained
for determining the presence/absence of toner, a toner presence
determination made when the toner density has changed only slightly
would tend to be erroneous.
To resolve this problem, in this embodiment, the threshold value
used in the toner presence/absence detection mode is properly
changed in accordance with the toner density sensitivity, which
fluctuates in accordance with the cumulative period for the use of
the developer. A specific control method will now be explained.
In the fourth embodiment, as in the first embodiment, a threshold
value Vtrgt is determined based on a patch image density signal
Vlast obtained, during normal operation, immediately before the
toner presence/absence detection mode is entered. An expression for
determining the threshold value Vtrgt is defined as follows.
Vtrgt=Vlast+B (3)
The coefficient B in expression (3) is a variable, and an
appropriate value is selected in accordance with the cumulative
period for the use of the developer. The period for the use of the
developer is obtained by counting the number of sheets that have
been processed. In another method for measuring the period for the
use of the developer, the period for rotation of the developing
sleeve 3 or the period for rotation of the agitation screw 2a or 2b
is counted, and an appropriate method is selected, depending on the
case. The relationship between the accumulated number of sheets
that have been passed and the coefficient B is shown in Table
2.
TABLE-US-00002 TABLE 2 The cumulative number of sheets processed
Coefficient B 0 or greater, and fewer than 10000 30 10000 or
greater, and fewer than 20000 33 20000 or greater, and fewer than
30000 36 30000 or greater, and fewer than 4,0000 39 40000 or
greater 42
When the threshold value Vtrgt is determined using expression (3),
the presence/absence of toner can be correctly detected, consequent
with the deterioration of the developer.
It should be noted that the coefficient B is not limited to the
values in Table 2, and an optimal value can be selected, depending
on the configuration of the image forming apparatus and the
developer that is employed.
As is described above, since for use in the toner presence/absence
detection mode, an appropriate threshold value is selected in
consonance with the toner density sensitivity of a developer for
which its deterioration accords with its cumulative period of use,
the presence/absence of toner can be correctly and stably detected,
regardless of the deterioration of the developer.
Fifth Embodiment
FIG. 9 is a schematic diagram showing the configuration of an image
forming apparatus according to a fifth embodiment of the present
invention. The image forming apparatus shown in FIG. 9 is an
electrophotographic, full color printer that uses four colors.
The configuration of the printer (hereinafter referred to as the
image forming apparatus) will now be described while referring to
FIG. 9.
The image forming apparatus in FIG. 9 comprises a drum-shaped,
electrophotographic, photosensitive member (hereinafter referred to
as a photosensitive drum) 101 that functions as an image bearing
member. The photosensitive drum 101 is supported so it is rotatable
in the direction indicated by an arrow R1. Around the periphery of
the photosensitive drum 101, arranged in order from upstream in its
rotational direction, are a primary charging device (charging
means) 102, an exposure apparatus (exposure means) 103, a
developing apparatus (developing means) 104, an intermediate
transferring belt 105 and a cleaning apparatus (cleaning means)
106. Further, positioned under the intermediate transferring belt
105 is a transferring and conveying belt 107, downstream of which,
in the direction in which recording material P is conveyed (a
direction indicated by an arrow A), is a fixing apparatus (fixing
means) 108.
In this embodiment, the photosensitive drum 101 has a diameter of
60 mm. As is shown in FIG. 10, to obtain the photosensitive drum
101, a photosensitive layer 101b, of a common organic
photoconductive (OPC) material, is formed on the outer surface of a
grounded, conductive drum base 101a, of aluminum, and a protective
layer (OCL) 101c, having a superior abrasion resistance, is
deposited on the photosensitive layer 101b. The photosensitive
layer 101b is in turn formed of four layers, a subbing layer (CPL)
101bl, an injection prevention layer (UCL) 101b2, a charge
generation layer (CGL) 101b3 and a charge transportation layer
(CTL) 101b4. The photosensitive layer 101b is normally an
insulating member, and is characterized in that it becomes
conductive when irradiated by light having a specific wavelength.
This occurs because positive holes (electron pairs) are generated
in the charge generation layer 101b3 by light irradiation, and
serve as charge carriers. The charge generation layer 101b3 is made
of polycarbonate, wherein 0.2 .mu.m of a phthalocyanine compound
has been dispersed, and the charge transportation layer 101b4 is
made of polycarbonate, wherein 25 .mu.m of a hydrazone compound has
been dispersed. The photosensitive drum 101 is rotated by driving
means (not shown) at a predetermined processing speed (a peripheral
velocity) in the direction indicated by the arrow R1.
In this embodiment, a corona discharging device of a scorotron type
is employed as the primary charging device 102. The corona
discharging device is formed by partially enclosing a discharge
wire 102a with a metal shield 102b that is open toward the
photosensitive drum 101.
A laser scanner for turning on or off a laser beam In accordance
with image data is employed as the exposure device 103 in this
embodiment. A laser beam emitted by the exposure apparatus 103
irradiates the surface of the electrified photosensitive drum 101
through a reflection mirror. Through this process, charges are
removed/ from the irradiated portion and an electrostatic latent
image is formed.
The developing apparatus 104 for this embodiment employs a rotating
development method, and includes: a rotary member 104A, which is
rotated by a motor (not shown) at a shaft 104a in the direction
indicated by an arrow R4; and four developing devices mounted on
the rotary member 4A, i.e., black, yellow, magenta and cyan
developing devices 104K, 104Y, 104M and 104C. To form a black
developer image (toner image) on the photosensitive drum 101, the
black developing device 104K performs the development process at a
development position D near the photosensitive drum 101. Similarly,
to form a yellow toner image, the rotary member 104A is rotated
90.degree. to move the yellow developing device 104Y to the
development position D for the development process. The same
operation is performed to form magenta and cyan toner images. In
the following explanation, unless a specific color is designated,
the developing device 104 is referred to.
The intermediate transferring belt 105 is extended around a drive
roller 110, a primary transferring roller (a primary transferring
and charging device) 111, a coupled roller 112 and a secondary
transferring opposed roller 113, and as the drive roller 110 is
rotated, is moved in the direction indicated by an arrow R5.
Further, a belt cleaner 114 contacts the intermediate transferring
belt 105. The transferring and conveying belt 107 is extended
around a drive roller 115, a secondary transferring roller 116 and
a coupled roller 117, and as the drive roller 115 is rotated, is
moved in the direction indicated by an arrow R7. The transferring
roller 108 includes a fixing roller 118, incorporating a heater
(not shown), and a pressure roller 120, which contacts the fixing
roller 118 from below.
The operation of the thus arranged image forming apparatus will now
be described.
In FIG. 9, the exposure apparatus 103 exposes the surface of the
photosensitive drum 101 that has been electrified by the primary
charging device 102, and forms an electrostatic latent image on the
photosensitive drum 101. The developing device 104, holding a
predetermined color developer (toner), attaches the toner to the
electrostatic latent image, forming a toner image on the
photosensitive drum 101. A primary transferring bias application
power source 111a applies a primary transferring bias to the
primary transferring roller 111, and the toner image is transferred
to the intermediate transferring belt 105.
For full-color image suing four colors, first, a black toner image
is formed on the photosensitive drum by the black developing device
104, and is transferred to the intermediate transferring belt 105.
After the primary transfer had been completed, toner remaining on
the surface of photosensitive drum 101 (residual toner) is removed
by the cleaning apparatus 106. Then, the rotary member 104A is
rotated at 90.degree., and the yellow developing device 104Y is
moved to the development position D and forms a yellow toner image
on the photosensitive drum 101. Thereafter, as the primary image
transfer, the yellow toner image is transferred to the intermediate
transferring belt 105 and is superimposed on the black toner image
thereon.
This operation is then performed for the magenta developing device
104M and the cyan developing device 104C, so that four, differently
colored toner images are superimposed on the intermediate
transferring belt 105. Thereafter, a second transferring bias is
applied to the second transferring roller 116, and as a secondary
image transfer, the four differently-colored toner images borne by
the intermediate transferring belt 105 are collectively transferred
to the recording material P that is conveyed along the transferring
and conveying belt 107.
The recording material P bearing the toner image is separated from
the transferring and conveying belt 107, and is heated and
pressurized by the fixing roller 118 of the fixing apparatus 108
and the pressure roller 120. As a result, the toner image is fixed
to the surface of the recording material P, and a four-color image
is obtained. After the secondary image transfer has been completed,
toner remaining on the intermediate transferring belt 105 (residual
toner) is removed by the belt cleaner 114.
For monochrome image forming, an electrostatic latent image formed
on the photosensitive drum 101 is developed by a developing device
104 that holds a predetermined color toner. The obtained toner
image is then transferred to the intermediate transfer belt 105
and, immediately afterwards, is transferred to the recording
material P. Thereafter, the recording material P bearing the toner
image is separated from the transferring and conveying belt 107,
and is heated and pressurized by the fixing apparatus 108 to fix
the toner image on the surface.
In this embodiment, an image density detection sensor 121 is
located downstream of the development position D and upstream of
the primary transferring roller 111 in the rotational direction of
the photosensitive drum 101, so that the image density detection
sensor 121 faces the surface of the photosensitive drum 101.
While referring to FIG. 11, an explanation will now be given for
the developing devices 104Y, 104M, 104C and 104K, in FIG. 9, that
are provided for the individual colors and are mounted to the
rotary member 104A. For each developing device 104, a two component
developer containing non-magnetic toner, about 8% by weight, and
magnetic carriers is retained in a developer container 122. The
toner density should be appropriately adjusted in accordance with
the charge amount of toner, which need not always be 8% by weight,
the carrier particle size, and the configuration of the image
forming apparatus.
When image development has exhausted the toner in developer, it is
replenished by obtaining an appropriate amount of toner from a
toner container 123, one of which is detachably positioned in the
vicinity of each developing device 104 in the rotary member
104A.
When a developing device 104 is moved to the development position
D, a development opening faces the photosensitive drum 101, and a
rotatable developing sleeve 124 is arranged so that it is partially
exposed at the development opening.
A fixed magnet 125, which is magnetic field generation means, is
enclosed in the developing sleeve 124. During the development
process, the developing sleeve 124, made of a non-magnetic
material, is rotated in the direction indicated by an arrow R24 in
FIG. 11, i.e., rotated downward in the direction consonant with the
gravitational force in the vicinity of the development opening.
Then, the developing sleeve 124 carries to the development opening
the two-component developer in the developing container 122, which
constitutes the developing device 104, while holding layers of the
developer. In this manner, the developer is supplied to the
development position D facing the photosensitive drum 101, and an
electrostatic latent image on the photosensitive drum 101 is
developed.
In order to maintain an appropriate amount of developer to be
carried to the development opening, a regulation blade (developer
regulation member) 126 is located upstream of the development
opening, in the rotational direction of the developing sleeve 124,
and faces the developing sleeve 124. Control of the thickness of
the developer laid on the developing sleeve 124 is provided by the
regulation blade 126.
After the electrostatic latent image has been developed, residual
developer is carried forward as the developing sleeve 24 is
rotated, and is collected at the developer container 122. In the
developer container 122, as developer agitation and carrying means,
a first circulating screw 127a and a second circulating screw 127b
are respectively arranged near and further from the developing
sleeve 124. These screws 127a and 127b circulate and agitate and
mix the developer in the developer container 122. It should be
noted that in this embodiment, as shown in FIG. 11, the first
circulating screw 127a circulates the developer from the rear to
the front while the second circulating screw 127b circulates the
developer from the front to the rear.
As the image formation number of sheets (the number of copies) is
increased, the toner in the two component developer is consumed,
and an amount of toner equivalent to the amount consumed is carried
along a replenishment path 128, leading from a developer supply
port 123a in the toner container 123 to a developer replenishment
port 122a in the developer container 122, to replenish the supply
of toner in the developer container 122. The toner is stored in the
developer container 122, upstream in the direction in which the
developer is circulated by the second circulating screw 127b, and
is then agitated and mixed with developer already present in the
developer container 122 and developer carried there by the first
circulating screw 127a, following the development process. The thus
agitated developer is then transported to the first circulating
screw 127a, and is again supplied to the developing sleeve 124.
Located along the replenishment path 128 is a replenishment screw
(toner replenishment means) 130. The rotation time for the
replenishment screw 130 is controlled by a CPU 129, the control
means, and the amount of toner required to replenish the developing
device 104 is adjusted in accordance with the rotation time.
A toner patch detection method for the embodiment will now be
explained.
When the image forming apparatus is initially installed, first, a
reference toner image (hereinafter referred to as a patch image) is
formed under image forming conditions based on a predesignated
environment table, stored in backup memory, wherein temperature and
humidity information and corresponding processing procedures are
entered, i.e., values are predesignated for processing conditions
such as exposure intensity and developing and transfer biases. That
is, the electrified photosensitive drum 101 is exposed to a laser
beam, and a patch latent image is formed on the photosensitive drum
101 and developed to obtain a patch image. This method is called a
digital patch image method. As another method, instead of using a
laser bean to expose the photosensitive drum 101, i.e., instead of
emitting light at an exposure level of zero, the contrast potential
for a patch latent image may be obtained based on a potential
difference between a developing bias and the potential of the
photosensitive drum 101 (the potential of a portion that is
electrified by the primary charging device 102 but is not exposed
by the exposing apparatus 103), and the patch latent image may be
developed to obtain a patch image. This is called an analog patch
image method. The amount of replenishing toner transported from the
toner container 123 to the developer container 122 is controlled by
the CPU 129, so that a predesignated target patch signal value is
equal to the density of a patch image used for toner replenishment,
which is detected during the density control process that is
performed thereafter, i.e., the target patch signal value is equal
to the sensor output value.
In this embodiment, a latent image formed by digital exposure is
called a digital latent image, and an image obtained by developing
the digital latent image is called a digital image. To distinguish
between these, a latent image to form a patch image without
performing the above described exposure is called an analog latent
image, and an image obtained by developing the analog latent image
is called an analog image. In the following explanation, these
terms are employed as needed.
According to the digital patch image method, however, the initial
state of the characteristics of the photosensitive drum 101,
especially its photosensitivity, is sometimes changed because of
deterioration, the result of employment over an extended period of
time, and environmental changes. Therefore, a difference exists
between an actual potential that is obtained by exposing the
photosensitive drum 101 to the laser beam emitted by the exposure
apparatus 103, and a potential that should be obtained in the
initial state, and because of this potential difference, the
density of an image formed on the photosensitive drum 101 is at
variance with a predetermined value. When toner is replenished In
accordance with a image density value arrived at by including this
error, the density of the toner in the developing device 104 will
fall outside a desired range, and due to the change in the image
density and toner fogging, an image fault will occur.
Furthermore, in order to reduce manufacturing costs and size, a
photosensitive member potential measurement sensor, which is an
expensive part having a highly specialized function, is not
provided, and the amount of replenishing toner is adjusted based
only on a patch image used for toner replenishment. Therefore,
variances in the density of the developer in the developing device
104 are especially increased, as is the load imposed on developer,
so that a barrier, such as the frequent occurrence of abnormal or
fogged images, and a reduction in the service life of the
developer, may occur.
In this embodiment, in order to eliminate variances in the
potential of a laser irradiated portion of the photosensitive drum
101, which are caused by changes in the photosensitivity
characteristics of the photosensitive drum 101, an analog patch
formation method is employed. According to this method, a patch
latent image for toner replenishment is formed at a stable
potential without laser exposure being performed, and is developed
to obtain a patch image (reference toner image).
As is described above, the rotation time for the replenishment
screw 130 is controlled by the CPU 129, and the amount of toner
supplied for replenishing the developing device 104 is adjusted In
accordance with the rotation time. Toner supply control means for
controlling the rotation time will now be specifically
described.
Since as the image forming operation is repeated, toner in the
developer container 122 is consumed and the toner density in the
developer is reduced, it is preferable that the toner density be
adjusted within a desired range by toner replenishment, as needed.
A system according to this invention employs both first toner
supply control means, for controlling the rotation time for the
toner replenishment screw 130 based on a video count value for an
image density signal included, for example, in an image data signal
for a document copy, and second toner supply control means, for
forming a standard toner image (a reference toner image) on the
photosensitive drum to detect the density signal of the reference
toner image using a density detection sensor, for comparing the
density signal value with a pre-stored initial reference signal
value, and for employing the comparison results to correct the
driving period for the toner supply unit, which is determined by
the first toner supply control means.
According to this system, a video counting method is mainly
employed to control the toner density. According to the video
counting method, the level of a signal output by an image signal
processing circuit is obtained for each pixel, and the number of
count values accumulated is the equivalent of the pixels for the
document size. In this manner, the video count value for one sheet
of the document is obtained (e.g., the maximum video count value
for one sheet of size A4 is 3884.times.106 at 400 dpi and 256
gradations). The video count value corresponds to the predicted
amount of toner that will be consumed, and an appropriate rotation
time for the replenishment screw 130 is determined based on a
conversion table representing the relationship between the video
count value and the rotation time for the toner replenishment screw
130. In accordance with the thus determined rotation time, toner is
replenished.
For this embodiment, the rotation time for the toner replenishment
screw 130 is selected only from among values integer times a
predetermined time unit (unit block replenishment). In this
embodiment, the rotation time for the toner replenishment screw 130
for each unit block is set at 0.3 seconds, and the rotation time
for the toner replenishment screw 130 for one image is set at 0.3
seconds, or an integer times this value. A specific toner
replenishment state is shown in FIG. 12.
When, for example, In accordance with the video count value, a
rotation time of 0.42 seconds is obtained from the conversion table
for the toner replenishment screw 130, and only one unit block is
to be replenished for one image during the next image forming
operation (the rotation time for the toner replenishment screw 130
is 0.3 seconds). The remaining rotation time, 0.12 seconds, for the
toner replenishment screw 130 is stored as part of a surplus, and
is added to the rotation time that is obtained based on the
succeeding video count value. This processing is shown in FIG.
13.
When the rotation time for the toner replenishment screw 130 is
limited only to values an integer times the predetermined unit
time, as one advantage, the amount of toner replenished at one time
can be stabilized. When a video count value is small, the rotation
time obtained for the toner replenishment screw 130 and that is
based on this is very much reduced. The short rotation time more
greatly affects the rising time and the trailing time for the drive
motor that drives the toner replenishment screw 130, and the amount
of toner replenished is not stabilized. Therefore, as in this
embodiment, when a constant rotation time is maintained for the
toner replenishment screw 130, the amount of toner replenished can
be stabilized.
According to the video counting method, when the actual amount of
toner consumption differs from the predicted amount, the density of
the developer is gradually shifted away from the appropriate range.
Therefore, it is preferable that the amount of toner replenished be
corrected by using a patch detection method (hereinafter referred
to as a patch detection mode) at predetermined intervals (each time
the image forming operation has been performed a predetermined
number of times). In this embodiment, a predetermined interval is
every fifty sheets for a document having a small size (e.g., an A4
portrait document).
When the image formation number of sheets reaches fifty and the
operating timing for the patch detection mode arrives, an
electrostatic latent image is formed on the photosensitive drum 101
for a reference toner image having predetermined dimensions, and is
developed by applying a predetermined development contrast voltage.
A density signal Vsig for the obtained reference toner image is
detected by an optical sensor, which is positioned facing the
photosensitive drum 101, and its value is compared with an initial
reference signal Vref that was previously stored in memory. When
Vsig-Vref<0, it is ascertained that the density of a patch image
is low, i.e., that the density of the developer is low. The amount
of toner required for replenishment and a corresponding rotation
time for the toner replenishment screw 130 are determined in
accordance with the difference between Vref and Vsig, and the
amount of toner required is corrected by adding the rotation time
to a rotation time that has been determined using the video
counting method. When Vsig-Vref.gtoreq.0, it is ascertained that
the density of a patch image is high, i.e., that the density of the
developer is high. The amount of unnecessary toner and a
corresponding halted time for the toner replenishment screw 130 are
determined in accordance with the difference between Vref and Vsig,
and the amount of toner required for replenishment is corrected by
subtracting the halted time from a rotation time that is determined
using the video counting method. Through this control process, the
toner density difference can be corrected. Processing performed by
using both the video counting method and the patch detection method
is shown in FIG. 14.
In this embodiment, the density signal for the reference toner
image is detected on the photosensitive drum 101. However, the
reference toner image formed on the photosensitive drum 101 may be
transferred to the intermediate transferring member 105 and
detected after the transfer has been completed, and the density
signal Vsig may be detected by the optical sensor positioned near
the intermediate transferring member 105.
When based on the detection results In the patch detection mode the
rotation time for the toner replenishment screw 130 is to be
increased, i.e., when the number of unit blocks to be replenished
is to be increased, as is shown in FIG. 15, only one block is added
for each image. That is, when based on the detection results
obtained in the patch detection mode ten unit blocks to be
replenished are to be added, instead of adding all these blocks,
one block is added for each image to complete a correction using
ten or more sheets. Through this processing, a sudden rise in the
toner density in the developing device 104 and the occurrence of a
fogged image and a broken line image can be prevented.
The toner presence/absence detection process for this embodiment
will now be described. In this embodiment, sensors for detecting
the presence/absence of toner are not provided for the toner
cartridges (toner containers) 123, and the sensor output used for
patch detection is also employed by the CPU 129 to detect or
determine the presence/absence of toner. When the CPU 129
determines that the amount of toner remaining in the toner
cartridge 123 is so small that succeeding image forming cannot be
performed, the CPU 129 inhibits the image forming process. That is,
the CPU 129 employs the detected density of the patch image to
determine not only the presence/absence of toner in the toner
cartridge 123, but also to determine whether the image forming
should be continued. In the configuration of this embodiment,
wherein toner cartridges are provided for the image forming
apparatus for toner replenishment as needed, the detected density
of the patch image is employed to determine the presence/absence of
toner in the toner cartridge 123. However, a toner hopper having a
large capacity may be provided for the image forming apparatus, and
the presence/absence of toner in the toner hopper may be determined
based on the detected density of the patch image. In this case,
toner from the toner cartridge is used to replenish the toner
hopper.
Through the above described operation, the cost required for the
toner presence/absence detection sensor can be eliminated. FIG. 15
is a flowchart showing the toner presence/absence detection
operation.
The value of density signal Vsig detected in the patch detection
mode (S1) is compared with a predesignated lower limit value Vlimit
for a density signal (S2) to determine whether the value of density
signal Vsig exceeds the lower limit value Vlimit. When the value of
density signal Vsig exceeds the lower limit value Vlimit, the CPU
129 determines that a sufficient amount of toner is present in the
toner cartridge 123, and the amount of toner to be used for
replenishment is corrected to add one block for each image as
described above (S3). When the value of density signal Vsig is
equal to or smaller than the lower limit value, the CPU 129
determines that the amount of toner remaining in the toner
cartridge 123 is reduced, and enters a residual toner amount
detection mode. Then, when the CPU 129 is shifted to this mode, the
CPU 129 inhibits image forming, and displays a message to this
effect on the liquid crystal display of the image forming
apparatus, or transmits a message to this effect through a network
cable to a personal computer, for example, that is connected to the
image forming apparatus.
The residual toner amount detection mode for this embodiment will
now be described while referring to FIG. 16.
First, the rotary member 104A is rotated to move the developing
device 104 entered in the residual toner amount detection mode.
The toner replenishment screw 130 is rotated four seconds (a period
that does not depend on the output of a patch sensor) to forcibly
perform the toner replenishment operation, and at the same time,
the developing device 104 is idly rotated four seconds, i.e.,
agitates the developer. Thereafter, a toner patch image is formed,
and the density signal Vsig for this image is detected by a sensor.
When the detected signal value exceeds the lower limit value
Vlimit, the residual toner amount detection mode is terminated and
the image forming inhibited state is shifted to the image forming
enabled state.
When the value of density signal Vsig still exceeds the lower limit
value Vlimit, the toner replenishment screw 130 is again rotated
four seconds, and the developer 104 is also idly rotated four
seconds. Then, a series of steps for forming a toner patch image is
again performed, and the density signal Vsig for this image is
detected by the sensor. When the detected signal value is equal to
or smaller than the lower limit value Vlimit, the above described
operation is repeated a predetermined number of times (H) (five
times in this embodiment).
When the operation is repeated the predetermined number of times
(five times) and the detected signal value is still equal to or
smaller than below the lower limit value Vlimit, the forced
replenishment operation is performed for a period shorter than the
period for the preceding forced replenishment operation, i.e., two
seconds. When the signal value detected at this time is equal to or
smaller than the lower limit value Vlimit, this forced
replenishment operation is repeated a predetermined number of times
(J) (five times in this embodiment).
When the thus detected signal value is still smaller than the lower
limit value Vlimit, the CPU 129 determines that there is no toner,
and outputs an exchange toner cartridges notification, i.e.,
outputs a signal requesting an exchange.
This signal is transmitted to the liquid crystal display that is
provided as display means at the upper portion of the main body of
the image forming apparatus. When the image forming apparatus is
connected to a personal computer through a network, and is
functioning as a printer, the signal may be output to the personal
computer through the network.
As is described above, and as is shown in FIG. 16, the forced
replenishment operation is performed five times for four seconds
each, and sequentially, is performed five times for two seconds
each. During each replenishment operation, the developer 104 is
idly rotated for four seconds.
As described for this embodiment, in the residual toner amount
detection mode, the time (the amount of toner replenished) wherein
the toner replenishment screw 130 is driven for each forced
replenishment operation is changed in accordance with the
repetition count for the step, so that the driving time at the
succeeding step is shorter than the driving time at the initial
step.
That is, since the toner density is lowered when the residual toner
amount detection mode is entered, the amount of toner replenished
one time is increased to quickly raise the toner density. When the
toner density is increased, to a degree, the amount of toner
replenished one time is reduced so as to gradually raise the toner
density.
As is described above, in the residual toner amount detection mode,
since the amount of toner replenished during one forced
replenishment operation is changed during the detection sequence
series, the presence/absence of toner can be determined within a
short period of time, erroneous detection of the presence/absence
of the toner can be prevented, and a sudden increase in the toner
density can be avoided.
If a large amount of toner is replenished during one forced
replenishment operation at the beginning of the residual toner
amount detection mode, the toner density is sharply increased, and
various problems, such as toner dispersion, image fogging and image
density defects, will occur.
Further, if a small amount of toner is replenished during one
forced replenishment operation, a sharp increase in the toner
density can be avoided, while more time will be required to raise
the toner density and there will be frequent downtimes.
When the CPU 129 determines there is no toner, a new, full toner
cartridge is loaded into the image forming apparatus. Then, the CPU
129 again enters the residual toner amount detection mode and
performs the steps and operations described above to determine the
presence/absence of toner. In this case, since the length of the
period extending from the toner cartridge exchange to the image
forming enabled state can be greatly reduced, erroneous detection
of the presence/absence of toner can be prevented, and sharp
increases in toner density can be avoided. Furthermore, an image
forming failure, which occurs when an image is formed on the first
sheet following the recovery to the image forming enabled state,
can be prevented.
As is described above in this embodiment, an image forming
apparatus can be provided that employs the toner patch detection
method to determine, within a short period of time, the
presence/absence of toner in a toner cartridge, that prevents
erroneous detections of the presence/absence of toner, and that
avoids sharp increases in toner density.
Sixth Embodiment
A sixth embodiment will now be described. Since the image forming
processing performed in this embodiment is substantially the same
as that in the fifth embodiment, no further explanation for that
will be given.
In the fifth embodiment, a patch image was formed for each time the
forced replenishment operation was repeated in the residual toner
amount detection mode. However, in the first half of the residual
toner amount detection sequence (corresponding to the operation for
the first embodiment wherein toner replenishment performed for four
seconds was repeated five times), the operation for the forcible
replenishment of a large amount of toner was performed in order to
quickly recover the toner density, to a degree. Therefore, very
rarely does the patch density reach a desired value (Vlimit) during
this period. Therefore, in the sixth embodiment, in the residual
toner amount detection sequence, first, the forced replenishment
operation is performed without a toner patch image being detected,
and after the toner density has been recovered, to a degree, the
forced replenishment operation is repeated, while the toner patch
detection is also performed. This processing will now be described
in detail while referring to FIG. 17.
First, a rotary member 104A is rotated to move a developing device
104 that has entered the residual toner amount detection mode.
Then, a toner replenishment screw 130 is rotated for twelve seconds
to forcibly replenish toner, while the developing device 104 is
also idly rotated for twelve seconds. During this period, toner
patch detection is not performed.
Thereafter, referring to FIG. 17, the forced toner replenishment
operation is performed for four seconds, and toner patch detection
is performed. When the detected signal value exceeds a lower limit
value Vlimit for a density signal, the residual toner amount
detection mode is terminated and the image forming enabled state is
set.
When the detected patch signal value is equal to or smaller than
the lower limit value Vlimit, the above operation is repeated a
predetermined number of times (J) (twice in this embodiment).
When the operation is repeated the predetermined number of times
(twice), and the detected signal value is still equal to or smaller
than the lower value limit Vlimit, another forced replenishment
operation is performed for a shorter period than the one above,
i.e., for two seconds. When the signal value detected thereafter is
equal to or smaller than the lower limit value Vlimit, this
operation is repeated a predetermined number of times (J) (five
times in this embodiment). When the signal value detected at this
time is still equal to or smaller than the lower limit value
Vlimit, it is determined that toner is absent, and a toner
cartridge notification is output (a signal requesting the exchange
is output).
As is described above, first, In the residual toner amount
detection sequence, a forced replenishment operation is performed
without a toner patch detection being performing, and after the
toner density has been recovered, to a degree, the forced
replenishment operation is repeated, while toner patch detection is
performed. Therefore, the performance of unnecessary toner patch
detection processes can be eliminated. And as a result, the amount
of toner consumed during the toner patch detection process is
reduced, as is the period during which image forming is inhibited
(the period wherein the operating mode is shifted to the residual
toner amount detection mode), i.e., downtime can also be
reduced.
Seventh Embodiment
A seventh embodiment will now be described. Since the image forming
process performed for this embodiment is substantially the same as
that for the first embodiment, no further explanation for it will
be given.
It is generally known that during the last period in the service
life of a developer the charging function performed by a carrier is
reduced because of deterioration.
In this case, wherein, for example, absence of toner is determined
and a new, full toner cartridge is loaded, toner replenishment
using the forced replenishment operation after the residual toner
amount detection mode has been completed is not satisfactorily
electrified, and sometimes, the fluctuation of image density
occurs.
Therefore, in this embodiment, when the presence of toner is
determined in the residual toner amount detection mode, as in the
fifth embodiment and the sixth embodiment, a developing device that
performed the process in the residual toner amount detection mode
is idly rotated for thirty seconds after the residual toner amount
detection mode is terminated. Through this process, when in the
last period of the service life of the developer a large amount of
toner is replenished in the residual toner amount detection mode,
the toner replenished is satisfactorily agitated with the
developer, especially the carriers, and friction charging is
appropriately performed. As a result, fluctuation of the image
density does not occur.
This application claims priority from Japanese 25 Patent
Application Nos. 2003-330054 filed Sep. 22, 2003 and 2003-330057
filed Sep. 22, 2003, which are hereby incorporated reference
herein.
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